[/
  Copyright 2011 - 2020 John Maddock.
  Copyright 2013 - 2019 Paul A. Bristow.
  Copyright 2013 Christopher Kormanyos.

  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[section:gmp_float gmp_float]

`#include <nil/crypto3/multiprecision/gmp.hpp>`

   namespace boost{ namespace multiprecision{

   template <unsigned Digits10>
   class gmp_float;

   typedef number<gmp_float<50> >    mpf_float_50;
   typedef number<gmp_float<100> >   mpf_float_100;
   typedef number<gmp_float<500> >   mpf_float_500;
   typedef number<gmp_float<1000> >  mpf_float_1000;
   typedef number<gmp_float<0> >     mpf_float;

   }} // namespaces

The `gmp_float` back-end is used in conjunction with `number` : it acts as a thin wrapper around the [gmp] `mpf_t`
to provide an real-number type that is a drop-in replacement for the native C++ floating-point types, but with
much greater precision.

Type `gmp_float` can be used at fixed precision by specifying a non-zero `Digits10` template parameter, or
at variable precision by setting the template argument to zero.  The typedefs mpf_float_50, mpf_float_100,
mpf_float_500, mpf_float_1000 provide arithmetic types at 50, 100, 500 and 1000 decimal digits precision
respectively.  The typedef mpf_float provides a variable precision type whose precision can be controlled via the
`number`s member functions.

[note This type only provides standard library and `numeric_limits` support when the precision is fixed at compile time.]

As well as the usual conversions from arithmetic and string types, instances of `number<mpf_float<N> >` are
copy constructible and assignable from:

* The [gmp] native types `mpf_t`, `mpz_t`, `mpq_t`.
* The `number` wrappers around those types: `number<mpf_float<M> >`, `number<gmp_int>`, `number<gmp_rational>`.

It's also possible to access the underlying `mpf_t` via the `data()` member function of `gmp_float`.

Things you should know when using this type:

* Default constructed `gmp_float`s have the value zero (this is the [gmp] library's default behavior).
* No changes are made to the [gmp] library's global settings, so this type can be safely mixed with
existing [gmp] code.
* This backend supports rvalue-references and is move-aware, making instantiations of `number` on this backend move aware.
* It is not possible to round-trip objects of this type to and from a string and get back
exactly the same value.  This appears to be a limitation of [gmp].
* Since the underlying [gmp] types have no notion of infinities or NaNs, care should be taken
to avoid numeric overflow or division by zero.  That latter will result in a std::overflow_error being thrown,
while generating excessively large exponents may result in instability of the underlying [gmp]
library (in testing, converting a number with an excessively large or small exponent
to a string caused [gmp] to segfault).
* This type can equally be used with [mpir] as the underlying implementation - indeed that is
the recommended option on Win32.
* Conversion from a string results in a `std::runtime_error` being thrown if the string can not be interpreted
as a valid floating-point number.
* Division by zero results in a `std::overflow_error` being thrown.

[h5 [gmp] example:]

[mpf_eg]

[endsect]
